The present invention relates to an automatic film rewinding device for a camera which automatically rewinds the film when the film has been wound a predetermined number of frames.
A variety of automatic film rewinding devices have been proposed and used commercially. One of the essential functions of such a film rewinding device is to detect when the film has been wound. If this detecting operation is inadequate, then the film will be rewound although there remain some frames which are not exposed.
In one example of the conventional automatic film rewinding devices, the fact that all the film has been pulled out of the film cartridge for a predetermined period of time is detected in correlation with the fact that the film feeding sprockets have been stopped for a predetermined period of time, and the film is rewound in response to this detecting operation. In this automatic film rewinding device, because the detecting circuit includes a timer device, the number of components thereof is relatively large and the circuitry is necessarily complex. Moreover, it is necessary to adjust the time measured by the timer device. If the adjustment is performed improperly, the automatic film rewinding may start earlier or later than it should. This problem arises also in a system in which, when the film winding motor is stopped upon completion of the photographing operation, it is detected whether or not the time required for energizing the motor to wind the film exceeds a predetermined value. Additionally, both of these systems suffer from the drawback that, when more than a predetermined number of frames has been exposed, in developing the film, the last frame is liable to be covered by the tape which is bonded to the film to hold the latter to the spool of the film cartridge.
In another system, when film is loaded in the camera, the number of frames of the film is set, and whenever the film is wound, the remaining number of frames is determined so that the film is rewound when the remaining number of frames becomes zero. However, the system is still disadvantageous in that, if the number of frames is erroneously set, or if the setting is changed during the photographing operation, then it is impossible to correctly detect when the film has been wound.